Application of specific electrical fields to spinal nerve roots, spinal cord, and other nerve bundles for the purpose of chronic pain control has been actively practiced since the 1960s. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field (or stimulation) to spinal nervous tissue (i.e., spinal nerve roots and spinal cord bundles) can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated tissue. More specifically, applying particularized electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, in the afflicted bodily regions. This paresthesia can effectively mask the transmission of non-acute pain sensations to the brain.
Successful pain management and the avoidance of stimulation in unafflicted regions necessarily require that the applied electric field or stimulation be properly positioned longitudinally along the dorsal column. Positioning of an applied electrical field relative to a physiological midline is also important.
Nerve fibers relating to certain peripheral areas extend between the brain and a nerve root along the same relative side of the dorsal column as the corresponding peripheral areas. Pain that is concentrated on only one side of the body is “unilateral” in nature. In contrast, pain that is present on both sides of a patient is “bilateral.” To address unilateral pain, electrical energy may be applied to neural structures on the side of a dorsal column that directly corresponds to a side of the body subject to pain. Accordingly, bilateral pain is typically treated through either an application of electrical energy along a patient's physiological midline or an application of electrical energy that transverses the physiological midline.
The applied electric field is commonly delivered through electrodes positioned external to the dura layer surrounding the spinal cord. The electrodes are typically carried by two primary vehicles: percutaneous leads and laminotomy leads.
Percutaneous leads commonly have a circular cross-section (typically in the range of 0.05 inches) and three or more, equally-spaced ring electrodes. Percutaneous leads are typically placed above the dura layer of a patient using a Touhy-like needle. For insertion, the Touhy-like needle is passed through the skin, between desired vertebrae, to open above the dura layer. For unilateral pain, percutaneous leads are positioned on a side of a dorsal column corresponding to the “afflicted” side of the body, as discussed above, and for bilateral pain, a single percutaneous lead is positioned along the patient midline (or two or more leads are positioned on each side of the midline). Because of their relatively small dimensions, percutaneous leads typically are implanted with a less-invasive method than used for laminotomy leads. Furthermore, a user has the ability to create a large variety of electrode array patterns by using a plurality of leads.
In contrast, laminotomy leads have a paddle configuration and typically possess a plurality of electrodes (for example, two, four, eight, or sixteen) arranged in one or more columns. The exposed surface area of the plurality of electrodes is commonly confined to only one surface of the laminotomy lead, thus facilitating a more focused application of electrical energy.
Laminotomy leads are typically implanted transversely centered over the physiological midline of a patient. In such position, multiple columns of electrodes are well suited to address both unilateral and bilateral pain, where electrical energy may be administered using either column independently (on either side of the midline) or administered using both columns to create an electric field which traverses the midline.
A multi-column laminotomy lead usually enables reliable positioning of a plurality of electrodes, and in particular, a plurality of electrode columns that do not readily deviate from an initial implantation position. Furthermore, they are capable of being sutured in place. So, there is less migration in the operating environment of the human body. Thus, they typically offer greater stability than percutaneous leads.
Given the relative larger dimensions of conventional laminotomy leads, a surgical procedure is usually required for implantation. The surgical procedure, or partial laminectomy, requires the resection and removal of certain vertebral tissue and often a portion of the vertebra to allow both access to the dura and proper positioning of a laminotomy lead.
When selecting whether to use percutaneous leads or a laminotomy lead, therefore, the surgeon balances the risks of a more invasive surgical procedure against the advantages of using a laminotomy lead.